The present invention relates to a device for actuating the gearbox associated with an engine, especially an automobile, and more particularly such a device comprising:
control means for controlling coupling means; PA1 a gearbox actuating member; PA1 a first shaft driven in rotation by the engine; PA1 a second shaft designed to drive the gearbox actuating member; PA1 coupling means for coupling the second shaft to the first shaft under the action of the control means; and PA1 uncoupling and return means for uncoupling the second shaft from the first shaft after the second shaft has rotated through a predetermined angle, and returning the second shaft to its initial position after it has been uncoupled from the first shaft; PA1 control means; PA1 a gearbox actuating member; PA1 a first shaft driven in rotation by the engine; PA1 a second shaft designed to drive the gearbox actuating member; PA1 coupling means for coupling the second shaft to the first shaft under the action of the control means; and PA1 uncoupling and return means for uncoupling the second shaft from the first shaft after the second shaft has rotated through a predetermined angle, and returning the second shaft to its initial position after it has been uncoupled from the first shaft; PA1 means for actuating a clutch which is located between the engine and the gearbox, these means being designed to be driven by the second shaft; PA1 means for determining the angle through which the engine is rocked with respect to a nominal operating position; and PA1 means for opposing the engagement of said clutch by its actuating means when the angle of rocking is greater than a predetermined angle.
Such a device is known from document FR-A-877 118.
In the device of this document, an input shaft is driven by the engine and carries a first series of plates of a plate-type friction clutch. The second series of plates of this clutch is carried by another shaft capable of driving an output shaft in rotation. A control member interacting with a screw and nut system allows the plates to be pressed together and thus allows the input shaft and the output shaft to be joined together in terms of rotation. The screw and nut system is made so that after the shaft carrying the second series of plates, and therefore the output shaft, have rotated by a certain amount, the pressure between the plates ceases and the input shaft and output shaft are thus declutched. A spring then returns the output shaft to its original position.
The aforementioned document makes no provision for actuating a clutch located in the traditional fashion between the engine and a mechanical gearbox, also using the device described.
The automatic control of such a clutch in fact involves serious difficulties. Indeed, after changing gear it is necessary to rematch the rotational speed of the engine to the speed of the vehicle so as to avoid abrupt jarring when letting the clutch back out.
This is particularly important when "downshifting" (shifting from one gear ratio to a lower ratio), when abrupt engagement of the clutch while the engine is idling leads to abrupt braking of the vehicle.
In the absence of an automatic gearshifting device, the driver in these cases on the one hand accelerates so as to bring the engine up to a sufficient speed and, above all, slows down his letting-out of the clutch in order to cause the latter to slip, so as to lead to a progressive slowing-down of the vehicle at the same time as correspondingly accelerating the rotational speed of the engine.